It depends upon your experience - the uphill can be quite a drag - and the rocks quite pointy pointy on the way down
Pack enough water and food, if you are thinking of doing then in that order, then as you have to ride a long way over - consider the Whytes instead - though the Wall is likely to be less busy as the Whytes is v popular
The downhill switchbacks on the Pen can be a bi daunting first time out - so don't be afraid of getting off - similar on bits of the Wall, and at the bottom of the Pen, the fording of the stream requires a little pace or you might get wet feet - I've avoided it so far
There is a jet spray in the car park - I think it needs change
I prefer the atmosphere (i.e. quiet) at the Pen end of Afan - but each to their own
Don't go off like a train - I ride a lot - but the flat lands of the South East are no prep for some long up hills
Oh- and stop occassionally and look at the view and say hi to other bikers!
Enjoy